A security light based on motion sensing with PIR (passive infrared) motion sensor is traditionally configured with three operating units to perform its function and provides a motion activated illumination. The three operating units are a light emitting unit, a PIR motion sensing unit and a power control unit. The power control unit is typically installed inside a wall mounted junction box which is further installed on an electric outlet. The light emitting unit and the PIR motion sensing unit are externally and separately installed on the junction box, both are electrically coupled to the power control unit inside the junction box.
The PIR motion sensing unit includes a condensing lens and a PIR motion sensor. The condensing lens may be a Fresnel lens, a dot lens or others. The Fresnel lens through its dimension and structural design collects and remotely converges IR (infrared) ray signals into a focal point where the PIR motion sensor is positioned to receive the focused IR ray signals generated from a moving body. The PIR motion sensor in conjunction with an IR ray signal detection circuitry detects and decides if the IR ray signals received represents a motion signal and outputs a voltage signal to the power control unit to turn on the light emitting unit for performing an illumination mode for a preset time duration before being turned off. The PIR motion sensing unit is typically connected to the junction box through an angle adjustable structure, such that it can be adjusted to a direction requiring detection of motion intrusion occurrence and the light emitting unit is accordingly turned on to achieve a purpose of security protection. A PIR motion sensing security light configured as above is characterized with a wide and adjustable detection angle, a capacity to perform a high lumens output and a long detection distance. One shortage is that, when the PIR motion sensing security light is used for indoor applications, such as in a storage room or in a basement, the assembly of the PIR motion sensing security light is a bit too bulky and may not be conveniently used for indoor applications as for outdoor applications. In addition, people generally do not need very high illumination level for security protection like the outdoor living need.
A related art U.S. Pat. No. 7,327,254B2 disclosed a PIR light bulb with sensing function to improve an installation convenience, however it reduced detection scope, loss of detection direction adjustable feature and lower lumens output for application of small space automatic lighting control. Further, the related art packaged three operating units together to form a convenient single compact piece in a shape of a light bulb design while keeping their functions independently performed with a reduced capacity. The three operating units, which include an LED (light emitting diode) light emitting unit, a PIR motion sensing unit and a power control unit, are scaled down to a mini scale and installed inside a hollow light bulb housing made of a glass or a plastic material. The light bulb housing also serves as a light diffuser for scattering and transmitting light emitted from the LED light emitting unit and is further constructed with a metallic screw-in lamp cap for adapting to an AC power source. The PIR motion sensing unit is positioned along a central space of the light bulb housing. The bottom of the PIR motion sensing unit is surrounded by LEDs (light emitting diodes) of the light emitting unit, and the top of the PIR motion sensing unit is configured with a small Fresnel lens slightly protruding out of the shell surface of the light bulb housing for receiving IR ray signals generated from an intruder. The detection angle and detection distance of the PIR motion sensor are determined by the curvature and surface area of the Fresnel lens designed. Since the Fresnel lens of the related art is substantially sized down to become a mini PIR motion sensing unit, the PIR light bulb is configured and limited to a much smaller detection angle and much shorter detection range. In addition, the PIR motion sensing unit is an opaque packaged component which is positioned along the central line of the light bulb housing, and therefore it creates a shadow effect in the center of the PIR light bulb. When the PIR light bulb is triggered to be turned on by the PIR motion sensing unit to emit LED light, the LED light therefore is partially blocked by the body of the PIR motion sensing unit. This arrangement in fact is a dilemma between optimizing a detection capacity and optimizing an illumination capacity. The larger the Fresnel lens is designed, the larger the shadow area blocks the illumination of the PIR light bulb.
To remedy the loss of the adjustable feature of the detection direction, the inventor of the above related art further disclosed a technology in U.S. Pat. No. 8,123,379B2 granted Feb. 28, 2012 in which a Fresnel lens detection head is redesigned to become an eyeball construction such that the Fresnel lens detection head becomes angle adjustable. It only improves the detection capacity of the PIR light bulb to a limited extent because the fundamental issue is still the conflicting constraint of choosing an adequate dimension of the Fresnel lens between maximizing a detection scope and minimizing the shadow effect blocked by the PIR motion sensing unit positioned in the central space of the PIR light bulb.
The PIR motion sensor reacts only to a moving IR source or a moving heat radiation object. A fixed heat source, even with a time variation in its intensity, does not trigger the PIR motion sensor to generate a PIR motion signal. For such reason, when the PIR motion sensor and an LED array are arranged together behind a light diffuser, the heat generated from LEDs will not affect a normal function of the PIR motion sensor in principle. Since there is no virtual need to maintain a direct touch connection between the Fresnel lens and the PIR motion sensor, it is hence feasible to knock down conventional one-piece structure of the PIR motion sensing unit into two mutually separated and remotely located components without affecting the functional performance of the PIR motion sensor. The Fresnel lens can be designed to integrate with the light diffuser or can be designed as a separate piece located behind the light diffuser, and on the other hand, the PIR motion sensor can be remotely located at a focal point on which the focused IR ray signals collected by the Fresnel lens are converged and surrounded by the LEDs. With such arrangement, the size and curvature of the Fresnel lens can be enlarged to maximize detection scope and detection distance, and there is no more solid body to block the LED light to cause a shadow problem. This is the technical background of the present disclosure which can release the constraint of Fresnel lens design and also eliminate the shadow problem.